1. Field of the Invention
The present invention relates generally to magnetic storage media and more particularly to flexible magnetic disks for use in data storage.
2. Background Art
With the development of micro-miniature circuitry the availability of computer techniques for applications of all types has greatly increased the need for usable data storage capability. Magnetic media have been the primary means of storing data for computer and data processing usages. Of the magnetic storage media, one of the most popular types is the flexible diskette.
Flexible diskettes are recording disks of a flexible material such as polyethylene teraphthalate ("PET"). One or both surfaces of the disk is coated with a material including magnetic particles, usually of gamma-ferric oxide (.gamma.Fe.sub.2 O.sub.3). The disk has a central hole for fitting upon a spindle in the disk drive mechanism. The entire disk is enclosed in an envelope which has apertures therethrough for receiving the spindle, for indexing, and for receiving the read/write head which transfers information to and from the magnetic medium.
Flexible diskettes are commonly used in commerce and have been the subject of numerous previous patents and applications. Among the U.S. patents dealing with flexible diskettes are U.S. Pat. No. 3,951,264, issued to Heidecker, et al., U.S. Pat. No. 4,152,740, issued to Stratton, U.S. Pat. No. 4,216,511, issued to Bilek, and U.S. Pat. No. 4,052,750, issued to Barber, et al.
One of the primary difficulties encountered in the use of flexible diskettes is the difficulty in centering the magnetic disk precisely on the spindle of the disk drive. Centering is of extreme importance because it is necessary that the same data be at exactly the same position with respect to the read/write head and the index point each time the disk is placed upon the spindle. If the disk is not precisely centered, the indexing for the read/write head will not operate properly. Variations in the centering of the disk may also make it necessary for the read/write head to scan a wider area, or track, to find the desired information. This limits the number of tracks which can be placed on a given disk.
Various prior art attempts have dealt with strengthening the spindle aperture of the magnetic disk. This has frequently been useful for extending the life of the disk. These devices have typically been in the form of flexible reinforcement rings placed around the spindle aperture in order to prevent the use of the spindle from damaging the aperture and thus rendering the disk unusable. Examples of aperture reinforcement devices are found in the Barber et al. patent, the Bilek patent, the Stratton patent and the Fortifier.TM. marketed by Inmac Corporation of Santa Clara, Calif.
However, none of the reinforcement devices for use with flexible diskettes address the specific problem of precise centering of the disk on the spindle and maintaining that degree of centering over the life of the disk. Presently utilized flexible disks, even those with reinforcing rings, have a tendency to get out of center. This reduces their useful life and limits the amount of data that can be stored thereon.
Centering problems have been very difficult to eliminate in flexible disks due to the physical properties of the disk material. The PET material prevalently used for flexible disks is characterized by poor punching ability in that precise aperture punching is difficult to achieve. The PET material also exhibits anisotropic expansion characteristics in response to environmental changes. The asymmetric expansion of the PET in response to changes in humidity and temperature are particularly manifested in the vicinity of the spindle aperture since the material is subjected to physical stresses in that vicinity.
Furthermore, many prior art disks, especially those with insulating reinforcing members, may have problems with static electricity build-up on the disk medium.